Contamination or so-called scaling is a well-known problem which may occur in many different applications in process industry. Scaling, often called also fouling, means generally deposition or accumulation of unwanted material on the surfaces of pipes, vessels, or other containers used for leading or storing flowable materials.
As a result of scaling, an extra layer of solid material is formed on such surface. Thereby, the free volume within the pipe or other container, open for the presence of a flowable material, is changed. This can lead to many problems. For example, changed shape of the free volume causes disturbances to the fluid flow. At least, the reduced cross-sectional area of the free inner volume of a process pipe increases the flow resistance through the pipe. In an extreme case, the pipe can be entirely clogged, thereby stopping the entire process at issue. In general, scaling is a common problem in various areas of process industry, causing significantly increased operational costs and production losses.
Material formed on the surfaces of process equipment by scaling must be removed from time to time. This can be very burdensome. Particularly when the extra material is formed by hydrocarbon bonding, it is typically very hard and extremely difficult to remove by mechanical processes. As an alternative to mechanical removal, different softening and releasing agents have been developed for various scaling materials. Instead of removing the formed scaling material afterwards, it is often more preferable to act proactively by preventing the scaling. For example, different chemicals can be used as scale inhibitors mixed with the flowable material to control the formation of inorganic hard scales. Use of such chemicals reduces the rate of scale formation and modifies the structure of the scale so that it is more easily removable. In any case, in order to prevent dramatic problems e.g. due to unexpected clogging of a process pipe, or to optimize the use of scale inhibitors, one should be able to monitor the scaling situation and its development in time.
On the other hand, another problem occurring in various industrial process equipment for leading and/or storing flowable materials is the wear of the walls of the pipelines and vessels. Wear may occur due to chemically aggressive materials reacting with the surfaces of the process equipment, but it can also result from simple mechanical abrasion caused e.g. by sand contained in a liquid flow. Similarly to scaling, also wear changes the volumes and flow conditions within the process equipment, and can thus affect adversely the processes. In an extreme case, wearing through of a wall of a pipeline or a vessel and the consequent sudden discharge of the flowable material to the exterior of the process equipment may result in severe accidents and high financial damages, and even injuries of persons. Similarly to scaling, also wear should thus be able to be monitored continuously.
Wear may also occur simultaneously with scaling. Therefore, it would be highly useful to have an efficient solution capable of on-line monitoring of those both phenomena.
In prior art, scaling and/or pipe wall wearing have been monitored or diagnosed e.g. with camera-based techniques, wherein a camera is installed in the process equipment to be analyzed, with acoustic (typically ultrasound) methods, or by simple mechanical methods in which special intelligent test objects are mounted onto the pipe walls. For example, EP 2115452 discloses as a specific example an apparatus and method for measuring scaling within a spiral wound membrane by transmitting acoustic signal into a tube, measuring the signal reflected from a material interface inside the tube, and comparing the measurement result with a reference signal from a known, clean tube.
The ultrasound and test object techniques are practically point measurements, limiting severely the applicability of the techniques. In camera-based techniques, the process must often be interrupted to perform the actual monitoring steps.
At the moment, there is no reliable on-line monitoring technique for detecting scaling and wear in an early stage. In particular, there is no efficient commercial solution available which could be used to monitor both of those harmful phenomena.